1. Technical Field
The present invention relates to a wireless transmission apparatus, a wireless transmission method and a computer program.
Priority is claimed on Japanese Patent Application No. 2009-222271, filed Sep. 28, 2009, the content of which is incorporated herein by reference.
2. Background Art
In conventional cases, a wireless transmission apparatus which handles continuous signal sequences such as PDH (Plesiochronous Digital Hierarchy) signal and SDH (Synchronous Digital Hierarchy) signal successively conducts wireless transmission/reception operations to transmit continuous signals without interruption and suspension. However, recent years, transformation from the networks which handle continuous signal sequences to the networks which handle discrete signal sequences, for example, Ethernet (registered trademark) signals have been increased, and in accordance with such a transformation, applications of conventional wireless transmission apparatuses which handle continuous signal sequences to transmission of discrete signal sequences are increasing.
When applying the wireless transmission apparatuses which handle continuous signal sequences to transmission of discrete signal sequences, such wireless transmission apparatuses continuously conducts wireless transmission/reception operations, that is, always conducts wireless transmission/reception operations regardless of whether or not there are transmission signals. Therefore, a certain amount of electric power is consumed regardless of an increase/decrease in the amount of traffic.
A method for resolving such a problem is proposed in which the electric power consumed by the wireless transmission apparatus is reduced by controlling the electric power for a wireless transmission based on the traffic amount.
For example, Patent Document 1 discloses a technique in which a wireless transmission apparatus selects a modulation method with the lowest transmission speed between modulation methods with a wireless transmission capacity which conforms to a traffic amount. Here, in the modulation method with a low transmission speed, a multi-level number of a modulation is small, and when the multi-level number is comparatively small, the bit-error ratio of a wireless transmission path is comparatively small. In other words, it is possible to conduct a transmission with a low bit error ratio when using a small electric power for transmission because the modulation method with a low transmission speed is used.
However, in the adaptive modulation control method in response to the above-described traffic amount, an adaptive modulation controlling operation follows instant changes of transmission signals. Therefore, if it is instantly determined that a large amount of wireless transmission capacity is necessary even when a large bandwidth is not necessary based on an average of the traffic amount, results of saving the electric power consumption can be insufficient because the transmission power is increased by conducting an extending operation on a wireless transmission capacity.    Patent Document 1: Japanese Patent Application, First Publication No. 2006-165939